Selective recessing to form a fully aligned via

ABSTRACT

A method of forming a semiconductor device having a vertical metal line interconnect (via) fully aligned to a first direction of a first interconnect layer and a second direction of a second interconnect layer in a selective recess region by forming a plurality of metal lines in a first dielectric layer; and recessing in a recess region first portions of the plurality of metal lines such that top surfaces of the first portions of the plurality of metal lines are below a top surface of the first dielectric layer; wherein a non-recess region includes second portions of the plurality of metal lines that are outside the recess region.

BACKGROUND

The present invention relates in general to semiconductor devicefabrication methods and resulting structures. More specifically, thepresent invention relates to fabrication methods and resultingstructures for a semiconductor device having a vertical metal lineinterconnect (via) fully aligned to a first direction of a firstinterconnect layer and a second direction of a second interconnect layer(i.e., M layers) in a selective recess region.

In contemporary semiconductor device fabrication processes, a largenumber of semiconductor devices and conductive interconnect layers arefabricated in and on a single wafer. The conductive interconnect layersserve as a network of pathways that transport signals throughout anintegrated circuit (IC), thereby connecting circuit components of the ICinto a functioning whole and to the outside world. Interconnect layersare themselves interconnected by a network of holes (or vias) formedthrough the wafer. As IC feature sizes continue to decrease, the aspectratio (i.e., the ratio of height/depth to width) of features such asvias generally increases. Fabricating intricate structures of conductiveinterconnect layers and vias within an increasingly smaller waferfootprint is one of the most process-intensive and cost-sensitiveportions of semiconductor IC fabrication.

SUMMARY

According to an embodiment of the present invention, a method offabricating a semiconductor device having a vertical metal lineinterconnect (via) fully aligned to a first direction of a firstinterconnect layer and a second direction of a second interconnect layerin a selective recess region is provided. The method can include forminga plurality of metal lines in a first dielectric layer; and recessing ina recess region first portions of the plurality of metal lines such thattop surfaces of the first portions of the plurality of metal lines arebelow a top surface of the first dielectric layer; wherein a non-recessregion includes second portions of the plurality of metal lines that areoutside the recess region.

According to another embodiment, a structure having a via fully alignedto a first direction of a first interconnect layer and a seconddirection of a second interconnect layer is provided. The structure caninclude a plurality of metal lines formed in a first dielectric layer;first portions of the plurality of metal lines recessed in a recessregion such that top surfaces of the first portions of the plurality ofmetal lines are below a top surface of the first dielectric layer; and anon-recess region including second portions of the plurality of metallines that are outside the recess region.

According to another embodiment, a method of fabricating a semiconductordevice having a via fully aligned to a first direction of a firstinterconnect layer and a second direction of a second interconnect layerin a selective recess region is provided. The method can include forminga plurality of metal lines in a first dielectric layer; recessing in arecess region a first portion of a first metal line such that a topsurface of the first portion of the first metal line is below a topsurface of the first dielectric layer, the first metal line adjacent toa first side of a second metal line; and recessing in a recess region afirst portion of a third metal line such that a top surface of the firstportion of the third metal line is below a top surface of the firstdielectric layer, the third metal line adjacent to a second side of thesecond metal line, wherein the first side and the second side areopposite sides of the second metal line; wherein a non-recess regionincludes second portions of the first metal line and the second metalline that are outside the recess region.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present invention is particularly pointed outand distinctly defined in the claims at the conclusion of thespecification. The foregoing and other features and advantages areapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 depicts a top-down view of a structure having a plurality ofmetal lines in a first dielectric layer after an initial fabricationstage according to one or more embodiments of the present invention;

FIG. 2 depicts a cross-sectional view along line A-A of FIG. 1 showing aselective recess region according to one or more embodiments of thepresent invention;

FIG. 3 depicts the cross-sectional view along line A-A after forming asacrificial nitride layer and a low temperature oxide layer on the firstdielectric layer according to one or more embodiments of the presentinvention;

FIG. 4 depicts the cross-sectional view along line A-A after depositinga tri-layer mask pattern on the low temperature oxide layer according toone or more embodiments of the present invention;

FIG. 5 depicts the cross-sectional view along line A-A after opening thetri-layer mask pattern and removing the sacrificial nitride layer andthe low temperature oxide layer according to one or more embodiments ofthe present invention;

FIG. 6 depicts the cross-sectional view along line A-A after forming aplurality of recessed metal lines according to one or more embodimentsof the present invention;

FIG. 7 depicts the cross-sectional view along line A-A after strippingthe remaining low temperature oxide layer and sacrificial nitride layerhard mask according to one or more embodiments of the present invention;

FIG. 8 depicts a cross-sectional view along line A-A after depositing acap on the first dielectric layer and in the recessed openings accordingto one or more embodiments of the present invention;

FIG. 9 depicts a cross-sectional view along line A-A after forming asecond dielectric layer on the cap according to one or more embodimentsof the present invention;

FIG. 10 depicts a cross-sectional view along line A-A after forming avertical metal line interconnect (via) fully aligned in a firstdirection of a first interconnect layer and a second direction of asecond interconnect layer within the selective recess region;

FIG. 11 depicts a top-down view of another structure after anintermediate operation of a method of fabricating a semiconductor devicehaving a fully aligned via according to one or more embodiments of thepresent invention;

FIG. 12 depicts a cross-sectional view of the structure along line A-Aof FIG. 11 according to one or more embodiments of the presentinvention;

FIG. 13 depicts the cross-sectional view along line A-A of FIG. 11 afteropening a tri-layer mask pattern and removing a sacrificial nitridelayer and a low temperature oxide layer according to one or moreembodiments of the present invention;

FIG. 14 depicts a cross-sectional view along line A-A of FIG. 11 afterstripping the remaining low temperature oxide layer and the sacrificialnitride layer hard mask according to one or more embodiments of thepresent invention;

FIG. 15 depicts a cross-sectional view along line A-A of FIG. 11 afterforming a vertical metal line interconnect (via) fully aligned in afirst direction of a first interconnect layer and a second direction ofa second interconnect layer within the selective recess regionsaccording to one or more embodiments of the present invention;

FIG. 16 depicts a top-down view of another structure after anintermediate operation of a method of fabricating a semiconductor devicehaving a fully aligned via according to one or more embodiments of thepresent invention;

FIG. 17 depicts a cross-sectional view along the line A-A of FIG. 16according to one or more embodiments of the present invention;

FIG. 18 depicts a cross-sectional view along line A-A of FIG. 16 afterdepositing an etch-resistant dielectric into a first recess and a secondrecess until the recesses are completely filled;

FIG. 19 depicts a cross-sectional view along line A-A of FIG. 16 afterforming a vertical metal line interconnect (via) fully aligned in afirst direction of a first interconnect layer and a second direction ofa second interconnect layer within the selective recess regionsaccording to one or more embodiments of the present invention;

FIG. 20 depicts a cross-sectional view of another structure, wherein aporous silicon carbonitride ((p)SiNCH) 2018 is formed on the capaccording to one or more embodiments of the present invention;

FIG. 21 depicts a top-down view of another structure, wherein a line endseparates a first metal line and a second metal line along a firstdirection according to one or more embodiments of the present invention;

FIG. 22 depicts a selective copper-liner wet recess (TaN/Co/Cu)according to one or more embodiments of the present invention; and

FIG. 23 depicts a selective copper-liner wet recess elemental map(TaN/Co/Cu) of a portion of FIG. 22 according to one or more embodimentsof the present invention.

DETAILED DESCRIPTION

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. It is notedthat various connections and positional relationships (e.g., over,below, adjacent, etc.) are set forth between elements in the followingdescription and in the drawings. These connections and/or positionalrelationships, unless specified otherwise, can be direct or indirect,and the present invention is not intended to be limiting in thisrespect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements. It should benoted, the term “selective to,” such as, for example, “a first elementselective to a second element,” means that a first element can be etchedand the second element can act as an etch stop.

For the sake of brevity, conventional techniques related tosemiconductor device and IC fabrication may or may not be described indetail herein. Moreover, the various tasks and process steps describedherein can be incorporated into a more comprehensive procedure orprocess having additional steps or functionality not described in detailherein. In particular, various steps in the manufacture of semiconductordevices and semiconductor-based ICs are well known and so, in theinterest of brevity, many conventional steps will only be mentionedbriefly herein or will be omitted entirely without providing thewell-known process details.

By way of background, however, a more general description of thesemiconductor device fabrication processes that can be utilized inimplementing one or more embodiments of the present invention will nowbe provided. Although specific fabrication operations used inimplementing one or more embodiments of the present invention can beindividually known, the described combination of operations and/orresulting structures of the present invention are unique. Thus, theunique combination of the operations described in connection with thefabrication of a via according to the present invention utilize avariety of individually known physical and chemical processes performedon a semiconductor (e.g., silicon) substrate, some of which aredescribed in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into four general categories, namely, filmdeposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Semiconductordoping is the modification of electrical properties by doping, forexample, transistor sources and drains, generally by diffusion and/or byion implantation. These doping processes are followed by furnaceannealing or by rapid thermal annealing (RTA). Annealing serves toactivate the implanted dopants. Films of both conductors (e.g.,poly-silicon, aluminum, copper, etc.) and insulators (e.g., variousforms of silicon dioxide, silicon nitride, etc.) are used to connect andisolate transistors and their components. Selective doping of variousregions of the semiconductor substrate allows the conductivity of thesubstrate to be changed with the application of voltage. By creatingstructures of these various components, millions of transistors can bebuilt and wired together to form the complex circuitry of a modernmicroelectronic device.

Fundamental to the above-described fabrication processes issemiconductor lithography, i.e., the formation of three-dimensionalrelief images or patterns on the semiconductor substrate for subsequenttransfer of the pattern to the substrate. In semiconductor lithography,the patterns are a light sensitive polymer called a photo-resist. Tobuild the complex structures that make up a transistor and the manywires that connect the millions of transistors of a circuit, lithographyand etch pattern transfer steps are repeated multiple times. Eachpattern being printed on the wafer is aligned to the previously formedpatterns and slowly the conductors, insulators and selectively dopedregions are built up to form the final device.

Turning now to a more detailed description of technologies relevant tothe present invention, the fabrication of very large scale integrated(VLSI) or ultra large scale integrated (VLSI) circuits requires aninterconnect structure including metallic wiring that connectsindividual devices in a semiconductor chip to one another. Typically,the wiring interconnect network consists of two types of features thatserve as electrical conductors, namely line features that traverse adistance across the chip, along with via features that connect lines indifferent levels. Typically, the conducting metal lines and vias arecomprised of aluminum or copper and are electrically insulated byinterlayer dielectrics (ILD). In the interconnect structure, laminationsof via interlayer films are referred to herein as “V” layers, andinterconnect interlayer films are referred to herein as “M” layers.

To improve performance, the semiconductor industry has repeatedly shrunkthe transistor gate length and the chip size. As a consequence theinterconnect structure that forms the metallic circuitry has alsoshrunk. As IC feature sizes continue to decrease, the aspect ratio,(i.e., the ratio of height/depth to width) of features such as viasgenerally increases. Fabricating intricate structures of conductiveinterconnect layers and vias within an increasingly smaller waferfootprint is one of the most process-intensive and cost-sensitiveportions of semiconductor IC fabrication.

To improve the manufacturability of lithography fabrication operations,advanced masks that incorporate phase-shifting and optical proximitycorrection have been employed. In addition, as the size scale of theseinterconnects decrease, overlay error between features in theinterconnect structure can lead to reliability issues. Overlay errorsresult from misalignment during the lithography process as the maskinvariably becomes misaligned with the underlying structure. Althoughoverlay errors can be mitigated by reworking the lithography operations,some level of overlay error is unavoidable.

Two failure modes for interconnects that can result from the overlayerrors of lithographic patterns are electro-migration (EM) and timedependent dielectric breakdown (TDDB). EM failure results when a voidforms in the conducting metal feature through metal diffusion leading toa short (or very high resistance) in the circuitry. The mechanism of EMis highly dependent upon the current density and the cross section ofthe metal features. If the wiring is constructed such that theintersection between a via and a line is too small, smaller voids formedby EM can lead to failure, which shortens the EM lifetime.

TDDB is a failure mode whereby the insulating materials (or layers) nolonger serve as adequate electrical insulators resulting in unintendedconductance between two adjacent metal features. This phenomenon ishighly dependent upon the electrical field between the metal featuresbecause regions with higher electrical fields are more susceptible toTDDB failure. Consequently, it is a design goal to control the spacingbetween conducting metal features to maintain electrical fields totolerable levels.

To combat via misalignment and the device failures associated therewith,it would be desirable if one could form a fully aligned via, which is avertical metal line interconnect that is fully aligned to a firstdirection of a first interconnect layer and a second direction of asecond interconnect layer. Some solutions to achieve a fully aligned viarequire either a global recess or a selective dielectric, i.e., abuild-up approach, or a combination of both methods. These approachesare associated with a plurality of processing and lithography problems,including, for example, a negative impact on typical back end of line(BEOL) structures. Recess approaches to achieve a fully aligned viastructure can create undesirably high incoming aspect ratios (ARs)having a narrow pitch, which can result in a non-ideal metal fill orultra low-k dielectric (ULK) line flop over. Creating these high aspectratios during reactive ion etching (RIE) presents its own challenges,such as hard mask selectivity. The required hard mask thicknessincreases as the AR increases. For ARs greater than about 3.0, therequired hard mask thickness becomes relatively large and the selectiveremoval of the hard mask becomes increasingly difficult. Recesssolutions can also have critical dimension dependence that negativelyaffects wide lines. Further, cap/ULK selectivity during the requireddielectric etches is also challenging, due to the need to aggressivelyscale cap thickness due to RC time constant concerns. Moreover, whilebuild-up approaches can achieve a fully aligned via, these approaches doso at the hard mask and are therefore subject to the overlay toleranceof lithography employed.

One or more embodiments of the present invention provide methods offabricating a semiconductor device having a via fully aligned to both afirst direction of a first interconnect layer and a second direction ofa second interconnect layer in a selective recess region. Because thevia alignment in the first direction is not done at the hard mask, thedescribed method is free of any overlay dependency from upstreampatterning associated therewith. The described method employs aselective recess process that mitigates via size variation throughcontainment by selective materials. Methods for fabricating a fullyaligned via in a selective recess region and the resulting structurestherefrom in accordance with embodiments of the present invention aredescribed in detail below by referring to the accompanying drawings inFIGS. 1-23.

FIG. 1 illustrates a top-down view of a structure 100 having a pluralityof metal lines formed in a first dielectric layer 104 during anintermediate operation of a method of fabricating a semiconductor devicethat will have a fully aligned via 1000 (shown in FIG. 10) formed in aselective recess region 106 according to one or more embodiments. Theselective recess region 106 overlaps a portion (e.g., 101A, 101B, 101C)of metal lines 102A, 102B, and 102C of the plurality of metal lines. Theremaining metal lines of the plurality of metal lines lie outside theselective recess region 106. A via landing site 108 delineates a regionwithin the selective recess region 106 where the via 1000 will bedeposited during a damascene metallization operation, which will bedescribed in greater detail later in this detailed description. Themetal lines 102A, 102B, and 102C are parallel to each other in a firstdirection 110. For ease of illustration and description, only some ofthe plurality of metal lines are depicted (e.g., metal lines 102A, 102B,102C, and two additional lines on either side thereof). However, it isunderstood that three or more metal lines can be utilized. Each of themetal lines 102A, 102B, or 102C includes a first portion 101A, 101B, or101C that is within the selective recess region 106, as well as a secondportion 103A, 103B, or 103C of the metals lines 102A, 102B, or 102C thatis outside the selective recess region 106. The areas of the structure100 that are outside the selective recess region 106 are, collectively,a non-recess region.

FIG. 2 illustrates a cross-sectional view of the selective recess region106 (shown in FIG. 1) of the structure 100 along the line A-A of FIG. 1during an intermediate operation of a method of fabricating asemiconductor device according to one or more embodiments. The metallines 102A, 102B, and 102C are shown deposited in the first dielectriclayer 104 formed on a substrate 200. FIG. 2 illustrates the portions101A, 101B, and 101C of the three metal lines 102A, 102B, and 102C thatare within the selective recess region 106.

A variety of methods can be used to form the intermediate structure 100illustrated in FIGS. 1 and 2. The metal lines 102A, 102B, and 102C canbe fabricated using any technique, such as, for example, a single ordual damascene technique. In one or more embodiments, the metal lines102A, 102B, and 102C are deposited in a dielectric layer by patterningthe dielectric layer with open trenches where the conductor should be.The trenches in the dielectric are formed using, for example, a reactiveion etching (RIE) technique. RIE is a type of dry etching which useschemically reactive plasma to remove a material, such as a maskedpattern of semiconductor material, by exposing the material to abombardment of ions that dislodge portions of the material from theexposed surface. The plasma is generated under low pressure (vacuum) byan electromagnetic field. Once the underlying oxide layer is patternedwith open trenches a thick coating of copper that significantlyoverfills the trenches is deposited on the oxide layer, andchemical-mechanical planarization (CMP) is used to remove the portion ofthe copper (known as overburden) that extends above the top of the oxidelayer. The remaining copper within the trenches of the oxide layer isnot removed and becomes the patterned metal lines 102A, 102B, and 102C.In one or more embodiments, the metal lines 102A, 102B, and 102C can beany conductive material such as, for example, copper (Cu), aluminum(Al), or tungsten (W).

In one or more embodiments, the metal lines 102A, 102B, and 102C can becopper (Cu) and can include a barrier metal liner (not shown). Thebarrier metal liner prevents the copper from diffusing into, or doping,the surrounding materials, which can degrade their properties. Silicon,for example, forms deep-level traps when doped with copper. An idealbarrier metal liner must limit copper diffusivity sufficiently tochemically isolate the copper conductor from the surrounding materialsand should have a high electrical conductivity, for example, tantalumnitride and tantalum (TaN/Ta), titanium, titanium nitride, cobalt,ruthenium, and manganese. It should be noted that the barrier metalliner is not required if the interlayer dielectrics insulating the metallines 102A, 102B, and 102C are not susceptible to copper diffusion.

The first dielectric layer 104 is formed over substrate 200 and caninclude any dielectric material such as, for example, porous silicates,carbon doped oxides, silicon dioxides, silicon nitrides, siliconoxynitrides, or other dielectric materials. The first dielectric layer104 can be formed using, for example, chemical vapor deposition (CVD),plasma enhanced chemical vapor deposition, atomic layer deposition,flowable CVD, spin-on dielectrics, or physical vapor deposition. Thefirst dielectric layer 104 can have a thickness ranging from about 25 nmto about 200 nm. The substrate 200 can be of any suitable substratematerial such as, for example, monocrystalline Si, SiGe, SiC, orsemiconductor-on-insulator (SOI).

FIG. 3 is a cross-sectional view after forming a sacrificial nitridelayer 300 on the first dielectric layer 104 and forming a lowtemperature oxide layer 302 on the sacrificial nitride layer 300. Thesacrificial nitride layer 300 can be any suitable material such assilicon nitride. The sacrificial nitride layer 300 is removable during awet etching process. For example, silicon nitride can be removed using abuffered hydrofluoric acid (BHF) etch. The low temperature oxide layer302 can be formed using a variety of known methods such as, for example,chemical vapor deposition, plasma enhanced chemical vapor deposition,atomic layer deposition, or physical vapor deposition. The sacrificialnitride layer 300 and low temperature oxide layer 302 serve as a hardmask over the first dielectric layer 104 and the metal lines 102A, 102B,and 102C.

FIG. 4 is a cross-sectional view after depositing a tri-layer maskpattern 400 on the low temperature oxide layer 302. The tri-layer maskpattern 400 includes a photoresist layer 402 selectively patterned withan opening 404 having a width W such that the photoresist layer 402 ison top of the second portions 103A, 103B, and 103C of the metals lines102A, 102B, and 102C (i.e., those portions of the metal lines that arebeyond or outside the selective recess region 106 as depicted in FIG. 1)and the remaining metal lines of the plurality of metal lines that lieoutside the selective recess region 106, but not on top of the firstportions 101A, 101B, and 101C of the metals lines 102A, 102B, and 102C(i.e., the portions of the metal lines that are under the opening 404and inside the selective recess region 106). The photoresist layer 402allows for the recessing selectivity of the first portions 101A, 101B,and 101C of the metal lines 102A, 102B, and 102C.

The tri-layer mask pattern includes an anti-reflective coating layer 406and an organic underlayer 408, the anti-reflective coating layer 406located in between the photoresist layer 402 and the organic underlayer408. The organic underlayer 408 is located directly on top of the lowtemperature oxide layer 302. The tri-layer mask pattern can be made ofany suitable materials and can be formed using any suitable methodology.In one embodiment, a silicon-based anti-reflective spin-on hard mask(Si-SOH) is deposited using a spin-on coating process. The Si-SOH is atri-layer hard mask including a photoresist formed on an organicanti-reflective coating, such as a silicon-containing anti-reflectivecoating (SiARC), which is formed on an organic planarization underlayer(OPL). In another embodiment, the tri-layer mask can be formed usingchemical vapor deposition (CVD) process. In still another embodiment, atri-layer mask is not used. Instead, a bilayer resist (BLR) process (notillustrated) is used to pattern the opening 404.

FIG. 5 is a cross-sectional view after opening the tri-layer maskpattern 400 and removing the sacrificial nitride layer 300 and the lowtemperature oxide layer 302 on top of the portions 101A, 101B, and 101Cof the three metal lines 102A, 102B, and 102C to expose surfaces 500A,500B, and 500C of the portions 101A, 101B, and 101C of the metal lines102A, 102B, and 102C. In one embodiment, strong oxygen plasma is used tostrip the lithographic stacks including the sacrificial nitride layer300 and the low temperature oxide layer 302.

FIG. 6 is a cross-sectional view after forming recessed openings 604A,604B, and 604C by recessing portions 101A, 101B, and 101C of the threemetal lines 102A, 102B, and 102C within the selective recess region 106below a top surface 602 of the first dielectric layer 104. The recessedopenings 604A, 604B and 604C can be formed using any etching technique,such as, for example, reactive ion etching (RIE) and/or wet etching. Inone embodiment, the recessing can be performed in a manner where thebulk of the metal lines can be removed in a separate operation from ametal barrier liner.

FIG. 7 is an expanded cross-sectional view along the line A-A of FIG. 1which includes metal lines 700A and 700B which are located outside ofthe selective recess region 106, as depicted in FIG. 1, after strippingthe remaining low temperature oxide layer 302 and sacrificial nitridelayer 300 hard mask over the plurality of metal lines to completelyexpose the top surface 602 of the first dielectric layer 104 and the topsurface 700 of the metal lines which were not recessed.

FIG. 8 is a cross-sectional view after depositing a cap 800 on the firstdielectric layer 104 and in the recessed openings 604A, 604B, and 604C.The cap can be semi-conformally formed using any suitable depositionprocesses, for example, chemical vapor deposition (CVD), plasma-enhancedchemical vapor deposition (PECVD), atomic layer deposition (ALD),evaporation, physical vapor deposition (PVD), chemical solutiondeposition, or other like processes. In some embodiments the cap is asilicon nitride, silicon carbonitride (SiNCH), or metal oxide.

In one embodiment, conventional plasma enhanced chemical vapordeposition (PECVD) in combination with cyclic deposition—plasmatreatment is used for forming the semi-conformal cap. Low radiofrequency (RF) plasma power is used to deposit ultra-thin (˜2 nm) SiNfilm using silane and ammonia as precursors. Post deposition plasmatreatment is performed to densify the film. Plasma nitridation isperformed to improve the density of the SiN layers. This process can berepeated until the desired cap thickness is achieved.

Back End of Line (BEOL) capacitance is primarily governed by twocomponents: the interlayer dielectric (ILD) and the dielectric barrierfilms. Lowering the dielectric constant of the barrier film can bepreferred for capacitance reduction over the uses of lower kdielectrics, due to mechanical considerations, integration challengesand reliability requirements. Thinning the cap layer can be desirablebecause the caps often have higher dielectric constants than theneighboring dielectric, especially when using ULK dielectric. Thin capsare less selective than thick caps, however, and a tradeoff betweenselectivity and capacitance must be made. The first generation ofdielectric cap that was integrated successfully with coppermetallization was SiN (k˜7). In some applications SiNCH (k˜5.3) can bepreferable to SiN due to its lower dielectric constant.

FIG. 9 is a cross-sectional view after forming a second dielectric layer900 on the cap 800. In some embodiments, the first dielectric layer 104and the second dielectric layer 900 are the same dielectric material.The second dielectric layer 900 can be formed using a variety ofsuitable methods, such as flowable chemical vapor disposition (CVD) orspin-on-dielectric processes.

FIG. 10 is a cross-sectional view of the structure 100 having a metalline interconnect (via) 1000 fully aligned to both a first direction 110(shown in FIG. 1) and a second direction 1001 in the selective recessregion 106. Metal lines 102A, 102B, 102C are deposited in a firstdielectric layer 104. The metal lines are parallel to each other in thefirst direction 110 and define a first interconnect level 1002. Theportions 101A, 101B, and 101C of the three metal lines 102A, 102B, and102C within the selective recess region 106 are recessed below a topsurface 602 of the first dielectric layer 104.

A trench 1006, which defines a second interconnect level 1004, and thevia 1000 can be formed using a typical BEOL single or dual damascenemetallization operation (V_(x)/M_(x+1) process). Any suitableself-aligned vertical interconnect access (SAV) scheme for forming aself-aligned via (SAV) damascene structure can be used to form a viaself-aligned in the direction perpendicular to the second direction 1001(i.e., the direction along the trench 1006). In some embodiments, thefirst interconnect level 1002 is orthogonal to the second interconnectlevel 1004, such that the direction perpendicular to the seconddirection 1001 is the first direction 110. In one or more embodiments, apattern trench first scheme is used wherein at least one trench 1006 isformed along the second direction 1001 on the second dielectric layer900 prior to the via 1000 metallization operation, such that the trench1006 allows the via 1000 to self-align perpendicularly to the seconddirection 1001.

The cap 800 on the first dielectric layer 104 ensures that the via 1000will self-align perpendicularly to the first direction 110 (i.e., toalign in the second direction 1001). During the via 1000 metallizationoperation, a via RIE removes a portion of the cap 800 to expose theportion 101B of metal line 102B. In some embodiments, the via RIEpartially erodes sidewalls 1008A and 1008B of the cap 800.Self-containment, however, leading to a reduced via 1000 size, ismaintained even if the sidewalls 1008A and 1008B are partially eroded.For example, if the via 1000 contacts the cap 800 while being depositedinto the via landing site 108 the via 1000 will not pass through the cap800 but will instead conform to the shape of the cap 800. As such, thecap 800 serves as a barrier between the via 1000 and the neighboringmetal lines that forces the via to self-align in the second direction1001, preventing a short from forming during the metallizationoperation. In this manner, the incoming via aspect ratio is reduced atthe expense of reducing the metal height in and around the via landingsite 108, resulting in an improved metal fill and a reduction in therisk of a ULK line flop over.

FIG. 11 illustrates a top-down view of another structure 1100 having aplurality of metal lines formed in a first dielectric layer 1104 duringan intermediate operation of a method of fabricating a semiconductordevice that will have a fully aligned via 1500 (shown in FIG. 15) formedin a via landing site 1108 according to one or more embodiments.Selective recess regions 1106A and 1106B overlap a portion (e.g., 1101Aand 1101B) of metal lines 1102A and 1102C of the plurality of metallines. The remaining metal lines of the plurality of metal lines lieoutside the selective recess regions 1106A and 1106B. Via landing site1108 delineates a region between the selective recess regions 1106A and1106B where the via 1500 will be deposited during a damascenemetallization operation, which will be described in greater detail laterin this detailed description. The metal lines 1102A, 1102B, and 1102Care parallel to each other in a first direction 1110. For ease ofillustration and description, only some of the plurality of metal linesare depicted (e.g., metal lines 1102A, 1102B, 1102C, and two additionallines on either side thereof). However, it is understood that three ormore metal lines can be utilized. Each of the metal lines 1102A and1102C includes a first portion 1101A and 1101B that is within theselective recess regions 1106A and 1106B, respectfully, as well as asecond portion 1103A and 1103B of the metals lines 1102A and 1102C thatis outside the selective recess regions 1106A and 1106B.

FIG. 12 illustrates a cross-sectional view of the structure 1100 alongthe line A-A of FIG. 11 during an intermediate operation of a method offabricating a semiconductor device having a fully aligned via. The firstdielectric layer 1104 can be formed on a substrate 1202. This viewillustrates the portions 1101A and 1101B of the metal lines 1102A and1102C that are within the selective recess regions 1106A and 1106B.

The structure 1100 includes a substrate 1202 below the first dielectriclayer 1104 and a sacrificial nitride layer 1204, a low temperature oxidelayer 1206, and a tri-layer mask 1216 including a photoresist layer1212, an anti-reflected coating layer 1210 and an organic underlayer1208 formed on the first dielectric layer 1104, in a like configurationand formed in a like manner as in the structure 100 depicted in FIG. 4.In this embodiment, however, the photoresist layer 1212 is selectivelypatterned with two openings 1214A and 1214B having widths W1 and W2,respectfully, such that the photoresist is not on top of the portions1101A and 1101B of the metal lines 1102A and 1102C (i.e., within theselective recess regions 1106A and 1106B as depicted in FIG. 11).

FIG. 13 is a cross-sectional view of the structure 1100 after openingthe tri-layer mask pattern 1216 (as depicted in FIG. 12) and removingthe sacrificial nitride layer 1204 and the low temperature oxide layer1206 on top of the portions 1101A and 1101B of the metal lines 1102A and1102C (i.e., within the selective recess regions 1106A and 1106B asdepicted in FIG. 11) in a like manner as in the structure 100 depictedin FIG. 5. In one embodiment, strong oxygen plasma is used to strip thelithographic stacks including the sacrificial nitride layer 300 and thelow temperature oxide layer 302. The portions 1101A and 1101B of themetal lines 1102A and 1102C are adjacent to, and on opposite sides of, ametal line 1304 which is not recessed. Recessed openings 1300 and 1302are formed by recessing portions 1101A and 1101B of the metal lines1102A and 1102C (as depicted in FIG. 11) within the selective recessregions 1106A and 1106B below a top surface 1304 of the first dielectriclayer 1104. The recessed openings 1300 and 1302 can be formed using anyetching technique, such as, for example, reactive ion etching (RIE)and/or wet etching. In one embodiment, the recessing can be performed ina manner where the bulk of the metal lines can be removed in a separateoperation from a metal barrier liner.

FIG. 14 is an expanded cross-sectional view along the line A-A of FIG.11 which includes metal lines 1401A, 1401B and 1401C which are locatedoutside of the selective recess regions 1106A and 1106B, as is depictedin FIG. 11, after stripping the remaining low temperature oxide layer1206 and sacrificial nitride layer 1204 hard mask in a like manner as inthe structure 100 depicted in FIG. 7. A cap 1400 is formed on the firstdielectric layer 1104 and in the first recess 1300 and in the secondrecess 1302, in a like manner as in the structure 100 depicted in FIG.8. The cap can be conformally formed using any suitable depositionprocesses, for example, chemical vapor deposition (CVD), plasma-enhancedchemical vapor deposition (PECVD), atomic layer deposition (ALD),evaporation, physical vapor deposition (PVD), chemical solutiondeposition, or other like processes. In some embodiments the cap is asilicon nitride, silicon carbonitride (SiNCH), or metal nitride.

A second dielectric layer 1402 is formed on the cap 1400, in a likemanner as is depicted in FIG. 9. In some embodiments, the firstdielectric layer 1104 and the second dielectric layer 1402 are the samedielectric material. The second dielectric layer 1402 can be formedusing any suitable method, such as flowable chemical vapor disposition(CVD) or spin-on-dielectric processes.

FIG. 15 is a cross-sectional view of the structure 1100 having a metalline interconnect (via) 1500 fully aligned to both a first direction1110 (shown in FIG. 11) and a second direction 1501 in the selectiverecess regions 1106A and 1106B. Metal lines 1102A, 1102B and 1102C aredeposited in a first dielectric layer 1104. The metal lines are parallelto each other in the first direction 1110 and define a firstinterconnect level 1502. The portions 1101A and 1101B of the metal lines1102A and 1102B within the selective recess regions 1106A and 1106B,respectfully, are recessed below the top surface 1304 of the firstdielectric layer 1104.

A trench 1508, which defines a second interconnect level 1504, and thevia 1500 can be formed using a typical BEOL single or dual damascenemetallization operation (V_(x)/M_(x+1) process). Any suitableself-aligned vertical interconnect access (SAV) scheme for forming aself-aligned via (SAV) damascene structure can be used to form a viaself-aligned in the direction perpendicular to the second direction 1501(i.e., the direction along the trench 1508). In some embodiments, thefirst interconnect level 1502 is orthogonal to the second interconnectlevel 1504, such that the direction perpendicular to the seconddirection 1501 is the first direction 1110. In one or more embodiments,a pattern trench first scheme is used wherein at least one trench 1508is formed along the second direction 1501 on the second dielectric layer1402 prior to the via 1500 metallization operation, such that the trench1508 allows the via 1500 to self-align perpendicularly to the seconddirection 1501.

The cap 1400 on the first dielectric layer 1104 guides the via 1500 toself-align perpendicularly to the first direction 1110 (i.e., the seconddirection 1501). For example, if the via 1500 contacts the cap 1400while being deposited into the via landing site 1108 (shown in FIG. 11)the via 1500 will conform to the shape of the cap 1400 and will not passthrough. As such, the cap 1400 serves as a barrier between the via 1500and the neighboring metal lines which forces the via to self-align inthe second direction 1501, preventing a short from forming during themetallization process.

In this embodiment, only the neighboring metal lines 1101A and 1101B,adjacent to the via landing site 1108, are recessed. As a result, a fullvia approach aspect ratio is maintained at the via landing site 1108without a corresponding spacing reduction between the first interconnectlevel and the second interconnect level. A full via approach aspectratio relaxes the cap/ULK selectivity requirement to achieve a desiredcapacitance because the via is landing on a taller site, which resultsin a higher capacitance. This method requires a more precise lithographythan that required by the process employed to form the structure 100 asdepicted in FIG. 10 and as described herein. In some embodiments thismethod (i.e., wherein only the neighboring metal lines are recessed) isreserved for portions of the overall lithography having a criticalcapacitance requirement.

FIG. 16 illustrates a top-down view of another structure 1600 havingmetal lines 1602A, 1602B, and 1602C parallel to each other in a firstdirection 1610, in a first dielectric layer 1604 during an intermediateoperation of a method of fabricating a semiconductor device having afully aligned via 1900 (shown in FIG. 19) according to one or moreembodiments. A via landing site 1606, between selective recess regions1608A and 1608B, delineates a region wherein the via 1900 will bedeposited during a damascene metallization operation. Selective recessregions 1608A and 1608B overlap a portion (e.g., 1601A and 1601B) ofmetal lines 1602A and 1602C of the plurality of metal lines. Theremaining metal lines of the plurality of metal lines lie outside theselective recess regions 1608A and 1608B. Via landing site 1606delineates a region between the selective recess regions 1608A and 1608Bwhere the via 1900 will be deposited during a damascene metallizationoperation, which will be described in greater detail later in thisdetailed description. The metal lines 1602A, 1602B, and 1602C areparallel to each other in a first direction 1610. For ease ofillustration and description, only some of the plurality of metal linesare depicted (e.g., metal lines 1602A, 1602B, 1602C, and two additionallines on either side thereof). However, it is understood that three ormore metal lines can be utilized. Each of the metal lines 1602A and1602C includes a first portion 1601A and 1601B that is within theselective recess regions 1608A and 1608B, respectfully, as well as asecond portion 1603A and 1603B that is outside the selective recessregions 1106A and 1106B.

FIG. 17 is a cross-sectional view along the line A-A of FIG. 16. Thestructure 1600 includes recessed portions 1601A and 1601B of metal lines1602A and 1602C (shown in FIG. 16) recessed below a top surface 1702 ofthe first dielectric layer 1604. The region above each of the recessedlines 1601A and 1601B defines a first recess 1704 and a second recess1706, respectively. The metal lines 1602A and 1602C are adjacent to, andon opposite sides of, a metal line 1602B which is not recessed. Therecessed portions 1601A and 1601B of metal lines 1602A and 1602C and theassociated first recess 1704 and second recess 1706 can be formed usingany etching technique, such as, for example, reactive ion etching (RIE)and/or wet etching.

The first dielectric layer 1604 is formed on a substrate 1710. A cap1712 is formed on the first dielectric layer 1604 and in the firstrecess 1704 and in the second recess 1706, in a like manner as in thestructure 100 depicted in FIG. 8. The cap can be conformally formedusing any suitable deposition processes, for example, chemical vapordeposition (CVD), plasma-enhanced chemical vapor deposition (PECVD),atomic layer deposition (ALD), evaporation, physical vapor deposition(PVD), chemical solution deposition, or other like processes. In someembodiments the cap is a silicon nitride, silicon carbonitride (SiNCH),or metal nitride.

FIG. 18 is a cross-sectional view of the structure 1600 after depositingan etch-resistant dielectric 1800 into the first recess 1704 and thesecond recess 1706 until the recesses are completely filled. Theetch-resistant dielectric 1800 forms a barrier between the two recessedportions 1601A and 1601B of metal lines 1602A and 1602C and the via 1900(shown in FIG. 19) deposited in a later metallization process. Theetch-resistant dielectric 1800 can be any dielectric with a highetch-resistance such as, but not limited to, a nitride or siliconnitride. The etch-resistant dielectric 1800 can also be a high-kdielectric having a dielectric constant greater than 4.0, 7.0, or 10.0.High-k dielectric materials include oxides, nitrides, oxynitrides,silicates (e.g., metal silicates), aluminates, titanates, nitrides, orany combination thereof. Examples of high-k materials include, but arenot limited to, metal oxides such as hafnium oxide, hafnium siliconoxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminumoxide, zirconium oxide, zirconium silicon oxide, zirconium siliconoxynitride, tantalum oxide, titanium oxide, barium strontium titaniumoxide, barium titanium oxide, strontium titanium oxide, yttrium oxide,aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. Thehigh-k material can further include dopants such as, for example,lanthanum and aluminum.

The etch-resistant dielectric 1800 can be formed by any suitabledeposition process, for example, chemical vapor deposition (CVD),plasma-enhanced chemical vapor deposition (PECVD), atomic layerdeposition (ALD), evaporation, physical vapor deposition (PVD), chemicalsolution deposition, or other like processes.

FIG. 19 is a cross-sectional view of the structure 1600 having a metalline interconnect (via) 1900 fully aligned to both a first direction1610 and a second direction 1910 in the selective recess regions 1608Aand 1608B. The structure 1600 is substantially similar to the structure1100 depicted in FIG. 15 and is formed in a like manner, except that thestructure 1600 includes the etch-resistant dielectric 1800 whichcompletely fills both the first recess 1704 and the second recess 1706.A second dielectric layer 1902 is formed on the cap 1712, in a likemanner as is depicted in FIG. 9. In some embodiments, the seconddielectric layer 1902 has a lower etch resistance than theetch-resistant dielectric 1800. In still other embodiments the seconddielectric layer 1902 has a lower dielectric constant than the firstdielectric layer 1604. Moreover, as these embodiments advantageouslyfill both the first recess 1704 and the second recess 1706 with theetch-resistant dielectric 1800, the likelihood of a non-ideal dielectricfill causing a void in either recess is reduced.

A trench 1904, which defines a second interconnect level 1906, and thevia 1900 can be formed using a typical BEOL single or dual damascenemetallization operation (V_(x)/M_(x+1) process). Any suitableself-aligned vertical interconnect access (SAV) scheme for forming aself-aligned via (SAV) damascene structure can be used to form a viaself-aligned in the direction perpendicular to the second direction 1910(i.e., the direction along the trench 1904). In some embodiments, afirst interconnect level 1912 is orthogonal to the second interconnectlevel 1906, such that the direction perpendicular to the seconddirection 1910 is the first direction 1610 (shown in FIG. 16). In one ormore embodiments, a pattern trench first scheme is used wherein at leastone trench 1904 is formed along the second direction 1910 on the seconddielectric layer 1902 prior to the via 1900 metallization operation,such that the trench 1904 allows the via 1900 to self-alignperpendicularly to the second direction 1910.

The cap 1712 on the first dielectric layer 1604 and the etch-resistantdielectric 1800 guide the via 1900 to self-align perpendicularly to thefirst direction 1610. The via 1900 cannot pass through either the cap1712 or the etch-resistant dielectric 1800 while being deposited intothe via landing site 1606 (shown in FIG. 16). As such, the cap 1712 andthe etch-resistant dielectric 1800 serve as a barrier between the via1900 and the neighboring metal lines which forces the via to self-alignin the second direction 1910, preventing a short from forming during themetallization process.

In some embodiments, the combination of the cap 1712 and theetch-resistant dielectric 1800 allows for a via upsize or for a viawhich at least partially overlays the etch-resistant dielectric 1800without causing a short during the metallization process. Vias tend tonaturally shift from 1 to 10 nm, with a shift of 5 nm fairly commonduring the metallization process. The via overlay 1908, whether due to avia upsize or to a natural shift in the via position, can be preventedfrom shorting the first interconnect level 1912 by the etch-resistantdielectric 1800.

FIG. 20 illustrates yet another embodiment of the present invention. Thestructure 2000 of this embodiment is formed in a like manner as thestructure 1600 as depicted in FIG. 17, except that in this embodiment aporous silicon carbonitride ((p)SiNCH) 2018 is formed on the cap 2016.Porous SiNCH advantageously serves as its own copper diffusion layer,obviating the need for any barrier metal liner, which saves space duringthe metallization operation.

The structure 2000 includes two recessed metal lines 2002A and 2002Brecessed below a top surface 2004 of a first dielectric layer 2006. Theregion above each of the recessed lines 2002A and 2002B defines a firstrecess 2008 and a second recess 2010, respectively. The metal lines2002A and 2002B are adjacent to, and on opposite sides of, a metal line2012, which is not recessed. The first dielectric layer 2006 is formedon a substrate 2014. A cap 2016 is conformally formed on the firstdielectric layer 2006 and in the first recess 2008 and in the secondrecess 2010, in a like manner as in the structure 100 depicted in FIG.8. The cap can be conformally formed using any suitable depositionprocesses, for example, chemical vapor deposition (CVD), plasma-enhancedchemical vapor deposition (PECVD), atomic layer deposition (ALD),evaporation, physical vapor deposition (PVD), chemical solutiondeposition, or other like processes. In some embodiments the cap is asilicon nitride, silicon carbonitride (SiNCH), or metal nitride.

In some embodiments the cap 2016 prevents a via (not depicted) depositedduring the following metallization operation from passing through a void2020 within either the first recess 2008 or the second recess 2010.PECVD low-k films with poor gap filling capabilities, such as, forexample, porous SiNCH, are often avoided in gap-filling applications. Asthis embodiment advantageously confines the porous SiNCH to recessedregions where the via will not land, porous SiNCH can be used in placeof some other dielectric having good gap-filling properties, but whichrequires a barrier metal liner. In some embodiments, the porous SiNCHcan be replaced with other low-k films having poor gap fillingcapabilities.

FIG. 21 illustrates yet another embodiment of the present invention. Thestructure 2100 of this embodiment is substantially similar to, andformed in a like manner as, the structure 1600 as depicted in FIG. 16,except that in this embodiment a line end 2102 exists which separates afirst metal line 2104 and a second metal line 2106 along a firstdirection 2112. Line end adjacent shapes can be complicated, requiringasymmetric lines or space reduced process windows. In this embodiment aplurality of line selective recess windows 2108A, 2108B, and 2108Cdefine areas for selectively recessing metal lines to control a via (notdepicted) deposited in a via landing site 2110 during a metallizationoperation from causing a short in accordance with any previousembodiment taught by this invention.

FIG. 22 illustrates a selective copper-liner wet recess (TaN/Co/Cu) inaccordance with one or more embodiments of the present invention. Thestructure 2200 demonstrates a wet recess process having a goodselectivity to ULK.

FIG. 23 illustrates a selective copper-liner wet recess elemental map(TaN/Co/Cu) of a portion of FIG. 22 in accordance with one or moreembodiments of the present invention. The structure 2300 demonstrates awet recess process having a good selectivity to ULK.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments described. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments described herein.

What is claimed is:
 1. A method comprising: forming a plurality of metallines in a first dielectric layer; planarizing the plurality of metallines to a top surface of the first dielectric layer; forming asacrificial nitride layer on the first dielectric layer; forming a lowtemperature oxide layer on the sacrificial nitride layer; forming atri-layer mask pattern on the low temperature oxide layer, wherein thetri-layer mask pattern includes a photoresist layer selectivelypatterned to form an opening such that the photoresist is on top of thesecond portions of the plurality of metal lines and is not on top of thefirst portions of the plurality of metal lines, the opening having awidth that exposes every metal line among the plurality of metal lines;recessing in a recess region first portions of the plurality of metallines such that top surfaces of the first portions of the plurality ofmetal lines are below the top surface of the first dielectric layer;wherein a non-recess region comprises second portions of the pluralityof metal lines located in a non-recess region that is located outsidethe recess region; and wherein the second portions of the plurality ofmetal lines are not recessed.
 2. The method of claim 1, wherein thetri-layer mask pattern further includes an anti-reflective coating layerand an organic underlayer, the anti-reflective coating layer located inbetween the photoresist layer and the organic underlayer, and whereinthe organic underlayer is located directly on top of the low temperatureoxide layer.
 3. The method of claim 1, further comprising opening thetri-layer mask pattern and removing the sacrificial nitride layer, thelow temperature oxide layer, and the tri-layer mask pattern on top ofthe first portion of the plurality of metal lines such that a surface ofthe first portion of the plurality of metal lines is exposed.
 4. Themethod of claim 1, further comprising: forming a cap on the firstdielectric layer and on the top surfaces of the first portions of theplurality of metal lines; and forming a second dielectric layer on thecap.
 5. The method of claim 4, wherein the cap is semi-conformallyformed using a flowable chemical vapor disposition (CVD) or aspin-on-dielectric process; and wherein the cap is a silicon nitride orsilicon carbonitride.
 6. The method of claim 4, wherein the firstdielectric layer and the second dielectric layer are the same material.7. The method of claim 4, wherein the metal lines are parallel to eachother in a first direction, further comprising: forming a trench along asecond direction on the second dielectric layer such that the trenchallows a via to self-align perpendicularly to the second direction; andwherein the cap on the first dielectric layer allows the via toself-align perpendicularly to the first direction.
 8. The method ofclaim 1, wherein forming the plurality of metal lines in the firstdielectric layer further comprises depositing copper into a plurality oftrenches in the first dielectric layer and planarizing the depositedcopper using a chemical-mechanical planarization (CMP) polishingprocess.
 9. The method of claim 1, wherein the opening exposes theentire upper surfaces of the first portions of the plurality of metallines.